An amplitude equalizer is a device that compensates for an undesired amplitude-frequency characteristic of a system or a device. An amplitude equalizer may be either active or passive. An active equalizer requires an external source of power, i.e., a source other than the signal that is being equalized, while a passive equalizer does not require an external power source. While it is known that an active equalizer can provide gain (i.e., an amplitude gain greater than 0 dB) to frequencies of the signal that are being equalized, a passive equalizer is known to provide a loss, an attenuation (i.e., an amplitude gain less than 0 dB), to frequencies of the signal that are being equalized. Some equalizers are also known to be tunable, that is, their amplitude-frequency characteristic can be adjusted, or changed, by resizing (physically and/or electrically) their components.
The transmission distance and operating bit-rate for any digital bit-rate system are limited by the bandwidth of the transmission channel used to transport the information to its desired destination. The limited transmission channel bandwidth has the effect of distorting and dispersing the pulse shape that is used to represent the digital information. This distortion has the effect of causing successive transmitted bit pulses to interfere with each other. This interference is commonly referred to as intersymbol interference (ISI) and has the deleterious effects of (1) limiting the transmission distance, (2) limiting the operating bit-rate, and (3) compromising the robustness of the received bit stream. All three of these deleterious effects can be mitigated by incorporating an amplitude-equalization scheme that counteracts these effects. However, it is difficult to find such a scheme which has a positive effect on all three of the deleterious effects yet which is not costly to implement, and which preferably is passive, tunable, and suitable for mounting on a printed circuit (PC) board via automated PC-board assembly techniques.